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KVM: x86: Fix single-step debugging

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commit 5cc244a20b86090c087073c124284381cdf47234 upstream.

The single-step debugging of KVM guests on x86 is broken: if we run
gdb 'stepi' command at the breakpoint when the guest interrupts are
enabled, RIP always jumps to native_apic_mem_write(). Then other
nasty effects follow.

Long investigation showed that on Jun 7, 2017 the
commit c8401dda2f0a00cd25c0 ("KVM: x86: fix singlestepping over syscall")
introduced the kvm_run.debug corruption: kvm_vcpu_do_singlestep() can
be called without X86_EFLAGS_TF set.

Let's fix it. Please consider that for -stable.

Signed-off-by: Alexander Popov <alex.popov@linux.com>
Cc: stable@vger.kernel.org
Fixes: c8401dda2f0a00cd25c0 ("KVM: x86: fix singlestepping over syscall")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alexander Popov 2019-01-21 15:48:40 +03:00 committed by Greg Kroah-Hartman
parent 74d609f091
commit 43473a6f67
1 changed files with 1 additions and 2 deletions
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3
arch/x86/kvm/x86.c
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@ -5524,8 +5524,7 @@ restart:
toggle_interruptibility(vcpu, ctxt->interruptibility);
vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
kvm_rip_write(vcpu, ctxt->eip);
if (r == EMULATE_DONE &&
(ctxt->tf || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)))
if (r == EMULATE_DONE && ctxt->tf)
kvm_vcpu_do_singlestep(vcpu, &r);
if (!ctxt->have_exception ||
exception_type(ctxt->exception.vector) == EXCPT_TRAP)